Lab 13 Subtractive Color Filters Paint Experiments with

Lab 13: Subtractive Color: Filters & Paint • • Experiments with Filters: Color Samples & Paints (“Pigments”) Mixing Paint Spectra of Light Sources

λ(nm) 400 500 B 600 G 700 R Intensity • Additive primary colors: Red, Green and Blue (RGB) • Subtractive primary colors: Cyan, Magenta and Yellow (CMY) Graphs are based on RGB 400 500 600 700 Wavelength (nm)

Absorption of light Screen Filter White Light Magenta filter absorbs green light White Light B G R B R Subtractive material M Additive perception

Filters (Pigments) • Absorb their complementary hue • Transmit (reflect) their own hue • Transmittance (reflectance) 1 0 Y B M C G R Ideal Magenta filter Reflectance Transmittance – Fraction of incident light passed through (reflected back) 1 0 Y M C B G R Ideal Yellow pigments

Real Filters 100 % 0 B 60 % G R 1 0 Y B M C G R Intensity 100 Transmittance Intensity Real filters transmit a fraction of incident light 100 0 B G R Spectral Ranges TM B (400 – 500 nm) 0. 6 G (500 – 600 nm) 0 R (600 – 700 nm) 0. 6

Caution • Probe – Misaligned probe ask your TA to reposition – Polished probe tip do not scratch (it's a $3000 research grade device!) • Plastic Filters – Wrinkle when heated under the halogen lamp – Set – Freeze – Remove • Place the filter on the filter holder • Freeze the screen using “snapshot • Remove the filter • ” feature Brushes – Wash them thoroughly for next section • Spills? – There paper towels on the sink counter

Paint 1 part + 2 parts = Y M C B G R Y M C 0 1 Y M C 0 B G R Use ideal paint reflectance, NOT from spectrophotometer! B Reflectance 1 0 G R Now find hue using color triangle